Transparent conductors are used on touch screens to enable human touch or gesture interactions with computers, smart phones, and other graphics-based screen interfaces. Touch screen devices can be made by patterning (e.g., printing) a conductive material into electrical traces on a flexible substrate. Patterning of the conductive material can be performed in a roll-to-roll process where the substrate is unwound, converting operations such as printing and drying/curing are performed, and then the patterned substrate is wound again into a roll for further transport and processing. The patterned conductive layers can be connected to electronic circuit components such as, for example, flexible circuits, to form an electronic touch sensor that can be used as a component of an electronic device.
There are several approaches to patterning the conductive materials for use in electronic assemblies such as, for example, touch sensors.
As one example of an approach, the conductive material can be printed directly to form a pattern from a dispersion or ink, using standard printing processes such as, for example, ink-jet, gravure, flexographic, or screen printing. This direct printing technique produces a pattern in one step, with minimal waste. However, variations in the print thickness due to defects such as ribbing and pinholes may produce unacceptable variations in conductivity, as well as negatively impacting the optics of the sensor.
As another example of an approach, the surface of the substrate can be uniformly coated with the conductive material by forming a substantially continuous conductive layer. A resist material is then printed on the conductive layer using printing processes such as, for example, flexographic printing, gravure printing, ink jet printing, screen printing, spray coating, needle coating, photolithographic patterning, and offset printing. The patterned resist material allows selective removal of portions of the conductive layer to create a desired pattern (subtractive patterning). Selective removal is often accomplished either by wet chemical etching or laser ablation.